This invention relates generally to x-ray methods and apparatus, and more particularly to methods and apparatus that provide Automatic Protocol Assistance.
In x-ray tomosynthesis, a series of low dose x-ray images is acquired over a range of x-ray beam orientations relative to an imaged object. This viewing of the object from different orientations allows depth information to be incorporated into the final image. This depth information is, of course, unavailable in conventional (projection) x-ray imaging.
A typical range of the number of projections acquired during a tomosynthesis exam is between 41-61, at a frame rate of up to 6 fps. The tissue thickness along the x-ray path varies significantly at different angles, and there is a great risk of exposure cut-off in Automatic Exposure Control (AEC) mode. If this happens, the image quality will be compromised. Therefore, tomosynthesis typically utilizes exposures in fixed mode.
However, fixed-mode exposure poses a workflow issue. To ensure consistent image quality from patient to patient, acquisition technique should be adjusted based on various patient thickness. Otherwise, under-exposure or over-exposure are likely to occur. The former will suffer from poor image quality while the latter risks over-exposing patients. But estimating the proper technique for different patients is a quite challenging task. The technologists today in US represent a large body of variations in terms of experience levels. Sometimes with some technologists with less experience, retakes are taken for single energy chest x-ray. For tomosynthesis, it may be that retakes will increase. So to minimize the dependency on technologist's experience when selecting the technique for patients seems to be an effective strategy for manufacturers, such as Automatic Exposure Control (AEC) by GE Healthcare of Wisconsin. However, as stated above, there is a great risk of exposure cut-off in AEC mode.
Therefore it is desirable to addresses this workflow issue by developing methods and apparatus to automatically provide protocol assistance to help to achieve the optimized technique for different patients.